Start by either removing the canister off your bike / or out of the box (for those who bought it new) and stick some masking tape to help for you to mark & realign where to drill for the screw-holes....

.... don't forget the bottom side too!

then grab a #3mm allen key to take off the screws @ the tip-end of the canister & set them aside (in a small box/bag preferably).. slowly pull the tip out & the "core" should come off with it.. here's how it looks..

The "core"..

WARNING!!.. You are dealing w/fiber glass.. this stuff is VERY ITCHY & can easily get onto your clothes!

with the "core" out of the canister... measure out how much you wanna cut off... I measured mine @ 2inches.. and use masking tape as a reference guide & also to help protect the canister when cutting..

{not pictured}
Then unravel the fiber-glass (it's not tied, just tightly wound) & you'll find the "Y" pipe.. you would then measure the SAMEmeasurement of cut to the "Y" pipe at the single inlet section..

You can use a grinder w/cutting wheel disk or Dremel w/cutting wheel disk to make the cuts

Then tightly pack the fiber-glass back (a friend can be useful here!) & tightly wound the string around the packed "Y" pipe... You would NOT have to trim the fiber-glass.. just shove it all in!

Then use the lines you made to help line up where to drill for the allen screws.. carefully drill out the holes... then slide in just the tip by itself to see if the holes you made line up (if it doesn't, no worries.. just grab a piece of 150grit sand paper & roll it up for it to fit through the hole.. and sand away the areas that needs clearance!

I was "test" fitting how it would sit inside the can w/all that un-trimmed fiber-glass... looks good!

Then attach the "core" back into the tip of the exhaust like so..

Once you got that... slide back the core w/tip attached, back into the canister (where the folds meet from the canister should be the top!)... while looking through it making sure it sits correctly @ the inside back inlet end & bolt everything back up!

By leaving the packing untouched.. it has actually made it more quiet! I kinda like it this way... still strong enough to alert "others" of your presence... and yet quiet enough for you to LOVE/ENJOY it!